Electromyographic responses of paraspinal muscles to postural disturbance with special reference to scoliotic children.

Background: Electromyographic (EMG) responses of erector spinae to a postural perturbation have been described and interpreted as an unloading reflex. Moreover, these responses have been found clearly and constantly abnormal in subjects presenting a progressive idiopathic scoliosis when compared with responses observed in subjects presenting a nonprogressive scoliosis or in normal subjects.

Objective: To investigate responses to obtain more precise information on their components, on their origin, and on their variations in scoliotic children.

Subjects: Thirteen scoliotic children, with 3 cases of fast progressive idiopathic scoliosis, as well as 3 healthy subjects.

Setting: The study was carried out at the Swiss Institute of Chiropractic in Bern Switzerland.

Methods: The subjects were standing on a specially constructed platform that could be suddenly tilted either to the right or to the left. Thoracic and lumbar paraspinal muscle activity was recorded with pairs of self-adhesive surface bipolar EMG electrodes. The responses were analyzed to detect components and study their time course and relative amplitude in successive trials; characteristics common to different subjects were looked for.

Results: The presence of short-latency responses and later activities following a postural perturbation was confirmed. In a given subject, these components vary in amplitude and time course from one trial to another. On the other hand, the differences found across subjects are not significantly different from those found within the various subjects.

Conclusion: Our results exhibit some differences with previous data. They lead to a different neurophysiological interpretation and they indicate that the stimulus and the responses need more precise analysis before being used as a diagnostic and prognostic tool in evolutive scoliosis.